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Date: Sat, 15 Mar 2003 10:29:54 -0600
From: Bruno Wolff III <bruno@wolff.to>
To: cliff@cliffmeyers.com
Cc: pgsql-sql@postgresql.org
Subject: Re: help with table constraint / check
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On Sat, Mar 15, 2003 at 07:38:20 -0800,
  cliff@cliffmeyers.com wrote:
> 
> What I want to do is set up a constraint / check so that when a record is added,
> it takes the parent_id being passed in the INSERT statement, looks at the record
> whose fs_id equals the parent_id, and makes sure that the fs_type for that record
> is 'dir' and not 'file'.
> 
> Can I do this with standard constraints or do I need to use some PL/pgSQL
> features? Anyone have a few hints? Thanks!

One way to do this is to add a column with the parent's file system
type (constrained to be 'dir') and then make the foreign key to the parent use
both the parent ID and the file system type.